For $1000, anyone can purchase mobile advertising to track your location, app use

also discovered that individuals who purchase the ads could see what types of apps their target was using. That could potentially divulge information about the person’s interests, dating habits, religious affiliations, health conditions, political leanings and other potentially sensitive or private information.

Someone who wants to surveil a person’s movements first needs to learn the mobile advertising ID (MAID) for the target’s mobile phone. These unique identifiers that help marketers serve ads tailored to a person’s interests are sent to the advertiser and a number of other parties whenever a person clicks on a mobile ad. A person’s MAID also could be obtained by eavesdropping on an unsecured wireless network the person is using or by gaining temporary access to his or her WiFi router.

The UW team demonstrated that customers of advertising services can purchase a number of hyperlocal ads through that service, which will only be served to that particular phone when its owner opens an app in a particular spot. By setting up a grid of these location-based ads, the adversary can track the target’s movements if he or she has opened an app and remains in a location long enough for an ad to be served — typically about four minutes, the team found.

Importantly, the target does not have to click on or engage with the ad — the purchaser can see where ads are being served and use that information to track the target through space. In the team’s experiments, they were able to pinpoint a person’s location within about 8 meters.

“To be very honest, I was shocked at how effective this was,” said co-author Tadayoshi Kohno, an Allen School professor who has studied security vulnerabilities in products ranging from automobiles to medical devices. “We did this research to better understand the privacy risks with online advertising. There’s a fundamental tension that as advertisers become more capable of targeting and tracking people to deliver better ads, there’s also the opportunity for adversaries to begin exploiting that additional precision. It is important to understand both the benefits and risks with technologies.”

An individual could potentially disrupt the simple types of location-based attacks that the UW team demonstrated by frequently resetting the mobile advertising IDs in their phones — a feature that many smartphones now offer. Disabling location tracking within individual app settings could help, the researchers said, but advertisers still may be capable of harvesting location data in other ways.

On the industry side, mobile and online advertisers could help thwart these types of attacks by rejecting ad buys that target only a small number of devices or individuals, the researchers said. They also could develop and deploy machine learning tools to distinguish between normal advertising patterns and suspicious advertising behavior that looks more like personal surveillance.

UW notes that the next steps for the team include working with experts at the UW’s Tech Policy Lab to explore the legal and policy questions raised by this new form of potential intelligence gathering.

The research was funded by The National Science Foundation, The Tech Policy Lab and the Short-Dooley Professorship.